In recent years, inkjet printing devices, including inkjet printers, fax machines, copiers, etc., have seen a very rapid growth and, whether at home or in office, they have become an integral part of our everyday life. The basic ink jet printing process involves one or more electrically driven ink jet printing heads. Each printing head contains a tiny discharge orifice which typically ranges from 40 to 50 microns, but can be from 10-200 microns. Typically the printing heads are energized by a magnetostrictive or piezoelectric means to emit a modulated stream of ink droplets, which are printed onto the printing (or recording) medium to form a replica of the image being transmitted. Ink jet printers (including fax machines, copiers, etc.) have several distinct advantages over other printing mechanisms such as laser jet printers in that, among other things, they involve very clean operations (i.e., do not require toners which can cause a mess if leakage occurs), do not need warm-up time, can be made very compact in size, require less parts and with much simpler construction, and are much less expensive than the laser jet printers. Continuous improvements in ink jet printers have further increased their popularity as well as widening their range of applications.
The overwhelming majority of the inks used in office ink jet printers belong to the water-soluble dye-based inks, which provide more vivid color than the pigment-based inks, but with relatively poorer water and light resistance. The printing or recording media, on which the jet streamed inks are printed or recorded, can be regular paper, coated paper, glossy paper, transparency, or even fabrics. One of the key factors affecting the print quality is the absorbability of the ink droplets by the printing medium. In order to obtain high-quality prints, there must be an optimum coordination between the print medium and the ink droplets.
Because water-soluble dye-based inks are the prevalent choice in the office ink jet printers, smearing on regular paper or transparency has been the major concern troubling ink jet users. Most of ink jet printing papers contain an ink absorption layer on a substrate. Because different types of substrates, which can be various types of papers or transparencies, exhibit different degrees of transparency, smoothness, porosity, whiteness, etc. in order for different types of applications, it is very difficult, if not impossible, to find an ink absorption layer that will fit different types of substrates. As discussed above, in order to obtain high-quality prints, there must be an optimum match between the print medium, mainly the absorption layer, and the ink droplets. Different types of printing media also exhibit different degrees of surface smoothness, anisotropicity, curl, and water resistance, etc. All these factors must be considered in the selection of the optimum ink. Typically, because there exist only limited choices with regard to the ink jet absorption materials for a given substrate, different types of inks are required in order to obtain the best results on a given type of printing medium. This is an expensive undertaking and usually cannot be afforded by the general public.
U.S. Pat. No. 4,300,820 discloses an absorption composition capable of absorbing more than 45% of its weight of water without dissolution at room temperature to form an optically clear hydrogel. The absorption composition contains 40 to 98 weight percent of water-soluble polymer of a vinyl lactam and 2 to 60 weight percent of a water-insoluble copolymer.
U.S. Pat. No. 4,369,229 discloses a laminated polymeric product in which one layer of the product is a polymeric blend capable of absorbing a large amount of water to form a hydrogel without dissolution at room temperature and the other layer adherent to the first, is a tough plastic or polymeric composition which is substantially inert to or resistant to water.
One of the shortcomings with the printing media disclosed in the '820 and '229 patents is that it contains a blend of water-soluble and water-insoluble polymers, which can cause phase separation by aging, causing a haze in the coated layer and a loss in transparency.
U.S. Pat. No. 4,503,111 discloses a recording material for ink jet printers comprising a hydrophobic substrate material with a leave polymeric coating, which is a mixture of polyvinylpyrrolidone and a compatible matrix-forming polymer, which can be gelatin or polyvinyl alcohol swellable by water and insoluble at room temperature but soluble at elevated temperatures. The printing medium disclosed in the '111 patent exhibited relatively inadequate water resistance and can become tacky in high humidity environment.
U.S. Pat. No. 4,935,307 discloses a hydrophilic polymeric blend which comprises at least one water-absorbing, hydrophilic polymeric material, at least one hydrophobic polymeric material having acid functionality, and at least one polyethylene glycol. The polymer blend provided improved durability and reduced curl which used as an image-receptive layer on graphic arts films. However, because of the relatively poor incompatibility between the polymers, phase separations can be observed, adversely affecting transparency.
Because of the large inherent advantages of ink jet printers and their immense potential market, it is important to develop improved printing medium for ink jet printers which can provide increased adhesion between the absorption layer and the substrate, so as to allow more flexible selections of the optimum absorption layers with regard to the various types of substrates, without having to compromise on other qualities such as curl, transparency, and water resistance.